The present invention relates to a piezoelectric actuator for precisely positioning an object, to a piezoelectric actuator for precisely positioning a thin-film magnetic head element used in a magnetic hard disk drive (HDD) and to a head gimbal assembly (HGA) with the precise positioning actuator.
In the magnetic HDD, thin-film magnetic head elements for writing magnetic information into and/or reading magnetic information from magnetic disks are in general formed on magnetic head sliders flying in operation above the rotating magnetic disks. The sliders are supported by suspensions of the HGAs at their top end sections.
Recently, recording and reproducing density along the radial direction or track width direction in the magnetic disk (track density) rapidly increase to satisfy the requirement for ever increasing data storage capacities and densities in today""s HDDs.
For advancing the track density, the position control of the magnetic head element with respect to the track in the magnetic disk by only a voice coil motor (VCM) has never presented enough accuracy. In order to solve this problem, another actuator is additionally mounted at a position nearer to the magnetic head slider than the VCM so as to perform fine precise positioning that cannot be realized by the VCK only. These techniques for realizing precise positioning of the magnetic head are described in for example U.S. Pat. No. 5,745,319 and Japanese unexamined patent publication No. 08180623A.
A typical structure of a conventional piezoelectric precise positioning actuator as the another actuator is shown in FIG. 1. This actuator called as a bimorph piezoelectric actuator has a metal plate or common electrode 12 sandwiched and adhered between two piezoelectric blocks 10 and 11, and drive electrodes 13 and 14 adhered to outer surfaces of the piezoelectric blocks 10 and 11, respectively. When electrical fields directed to opposite directions with each other are produced in the piezoelectric blocks 10 and 11 by respectively applying voltages with opposite phases between the drive electrode 13 and the common electrode 12 and between the drive electrode 14 and the Common electrode 12, these blocks 10 and 11 will expand and contract, respectively, causing the actuator to bend in a direction perpendicular to the electrodes.
However, this bimorph piezoelectric actuator can be formed only in a simply shaped single layer structure as shown in FIG. 1. Namely, it is very difficult to realize a piggyback bimorph multi-layered actuator with a shape of a tuning fork due to its complicated shape, weak mechanical strength depending upon the stacked direction and complicated layout of external electrodes.
Japanese examined patent publication No. 10225146A discloses a unimorph piezoelectric actuator with piezoelectric ceramics layers stacked on a non-piezoelectric bottom ad. The thicknesses of the respective stacked piezoelectric ceramics layers are gradually thinned in order outward from the bottom layer, the piezoelectric constants du of the respective stacked ceramics are gradually increased in order outward from the bottom layer, or the voltages applied to the respective stacked ceramics layers are gradually increased in order outward from the bottom layer so that the stacked ceramics layers bend toward the stacked direction.
However, since this bimorph piezoelectric actuator has to a stack piezoelectric ceramics layers with gradually differed thicknesses, gradually differ ed piezoelectric constants du or gradually differed applied voltages, not only the structure increases in complexity but also the manufacturing process becomes very complicated.
The assignee of the instant application has already proposed a piggyback unimorph actuator shown in FIG. 2. This piggyback actuator has two fixing parts 20 and 21 at its end sections and two rod shaped beam parts 22 and 23 arranged in parallel for coupling these fixing parts 20 and 21. An air gap 24 is formed between these beam parts 22 and 23. The fixing parts 20 and 21 have a larger width than that of the beam parts 22 and 23 so that sufficient fixing force can be ensured. Thus, the actuator is formed ion a tuning fork shape. The actuator has a stacked structure fabricated by alternately stacking one piezoelectric layer with a common electrode formed thereon and another piezoelectric layer with a drive electrode formed thereon. By applying voltages with the reversed phase across the drive electrode and the common electrode of the beam part 22 and across the drive electrode and the common electrode of the beam part 23, these beam parts will expand and contract, respectively, causing the actuator to bend in a plane of the electrodes.
However, since the air gap 24 between the beam parts 22 and 23 in this piggyback unimorph actuator shown in FIG. 2 is very narrow as about 50 xcexcm for example, it is necessary to use an expensive microfabrication process such as a powder-beam etching process which utilizes very fine grains for fabricating the actuator causing the manufacturing cost to greatly increase. Also, since there is a limit in fabrication of the narrower air gap, a larger bending amount or a larger stroke of displacement of the actuator cannot be expected. In addition, such air gap will remarkably reduce the shock resistance of the actuator itself.
It is therefore an object of the present invention to provide an actuator for precisely positioning an object, an actuator for precisely positioning a thin-film magnetic head element and a HGA with the precise positioning actuator, whereby simple structure and easy manufacture of the actuator can be expected.
Another object of the present invention is to provide an actuator for precisely positioning an object, an actuator for precisely positioning a thin-film magnetic head element and a HGA with the precise positioning actuator, whereby high shock resistance of the actuator can be expected.
Further object of the present invention is to provide an actuator for precisely positioning an object, an actuator for precisely positioning a thin-film magnetic head element and a HGA with the precise positioning actuator, whereby stroke of displacement can be easily controlled and large stroke of displacement can be expected.
According to the present invention, an actuator for precisely positioning an object to be positioned is provided. This actuator is fixed between the object and a support member and has a displacement generation part. The displacement part includes a solid piezoelectric material member, a common electrode formed on one surface of the piezoelectric material member to cover substantially whole of the one surface, and first and second electrodes formed on the other surface opposite to the one surface, of the piezoelectric material member to superimpose to the common electrode. The first and second electrodes have side edges facing with each other via a uniform width space, respectively.
Also, according to the present invention, an actuator for precisely positioning at least one thin-film magnetic head element to be positioned is provided. This actuator is fixed between a magnetic head slider with the at least one thin-film magnetic head element and a support member and has a displacement generation part. The displacement part includes a solid piezoelectric material member, a common electrode formed on one surface of the piezoelectric material member to cover substantially whole of the one surface, and first and second electrodes formed on the other surface opposite to the one surface, of the piezoelectric material member to superimpose to the common electrode. The first and second electrodes have side edges facing with each other via a uniform width space, respectively.
Furthermore, the present invention provides a HGA including a magnetic head slider with at least one thin-film magnetic head element, an actuator fixed to the magnetic head slider for performing precise positioning of the at least one thin-film magnetic head element, and a support member for fixing and supporting the actuator. The actuator has a displacement generation part. This displacement part includes a solid piezoelectric material member, a common electrode formed on one surface of the piezoelectric material member to cover substantially whole of the one surface, and first and second electrodes formed on the other surface opposite to the one surface, of the piezoelectric material member to superimpose to the common electrode. The first and second electrodes have side edges facing with each other via a uniform width space, respectively.
A common electrode and first and second electrodes or drive electrodes are formed on the opposite surfaces of a piezoelectric material member, respectively. Each of the first and second electrodes has a side edge. These side edges faces with each other via a uniform width space or slit. This uniform width space or slit between the first and second electrodes provides the similar functions as that of the air gap of the conventional actuator shown in FIG. 2 to produce substantially the same bending displacement in a plane of the electrodes as the conventional actuator without forming the air gap.
Since there is no air gap in the displacement generation part and it is possible to fabricate the this part only by printing the electrodes on the piezoelectric material member, the manufacturing process becomes very simple. Thus, manufacturing time and cost of the actuator can be remarkably reduced.
Also, since there is no air gap, the shock resistance of the actuator can be extremely increased.
Furthermore, since the width of the space or slit between the first and second electrodes can be adjusted by controlling the printing of the electrodes, the stroke of displacement of the actuator can be very easily controlled. In addition, since the spacing can be reduced to a limit of the printing technology, a larger bending amount or a larger stroke of displacement of the actuator can be easily obtained.
It is preferred that the common electrode and the first and second electrodes are substantially symmetric with respect to a center line of the piezoelectric material member.
It is preferred that the displacement generation part consists of a single layer structure of the piezoelectric material member, the common electrode formed on one surface of the single layer structure piezoelectric material member, and the first and second electrodes formed on the other surface opposite to the one surface of the single layer structure piezoelectric material member, or the displacement generation part consists of a multi-layered structure of plurality of stacked the piezoelectric material members, the common electrode formed on one surface of each of the multi-layered structure piezoelectric material members, and the first and second electrodes formed on the other surface opposite to the one surface of each of the multi-layered structure piezoelectric material members. If the displacement generation part has the multi-layered structure as the latter case, the voltage for driving the actuator can be lowered. Also, this multi-layered structure can be fabricated by simply stacking the piezoelectric material layers resulting the manufacturing processes to greatly simplify.
It is also preferred that the displacement generation part has a substantially rectangular parallelepiped shape.
It is preferred that the actuator further comprises fixing parts coupled to both ends of the displacement generation part. In this case, more preferably, the fixing part has a substantially rectangular parallelepiped shape with a width equal to or larger than a width of the displacement generation part.